Ballistic and guided missiles are effective high technology weapons. Employing anti-missiles in defense to shoot down ballistic or guided missiles provides, at best, only partial protection. As example, anti-missile defense systems that are radar dependent for detection and guidance have been shown to have significant drawback.
Multiple or single ballistic missiles may be launched simultaneously from sites into a prescribed trajectory toward a target and the missile or missiles are tracked by radar sensing systems that guide anti-missiles for destroying the hostile missles. A successful hit can produce missile debris that in the zone of the defense system or coming subsequent attack missiles may escape radar sensing system due to debris floating around the defense zone. A significant problem is that the anti-missile may miss the hostile missile's warhead, hitting instead another part of the missile's body. This leaves the warhead intact and a continued threat. Other shortcomings relate to controlling the timeliness of the anti-missiles' engagement with the attack missile, ensuring, for obvious reasons, that the hit, if made, occurs well out of range of the target.
Cruise and guided missiles present even greater challenges to anti-missile missile defense system. Typically such missiles travel close to the ground and follow the contour of the landscape, leaving little time to launch an anti-missile once the attacking missile is detected.
Lasers have proven to be effective in engaging and destroying hostile ballistic and guided missiles before they than can hit the target. The missile must initially be acquired by radar and the tracking transferred to an optical tracker. Once optically acquired and tracked, the system operates independently of radar. The defensive laser is not radar-dependent for tracking incoming missiles. Using infra-red type fine tracking sensor detection and aiming equipment, avoids the limitations of radar. Infra-red energy essentially travels in a straight line. It is easier to use and employ than radar. The fine track sensor performs quickly and may be readily and effectively linked to aim a laser weapon.
In areas in which atmospheric effects do not come into play, such as in outer space, the laser would be particularly effective. The use of infra-red aimed high power lasers avoids the deficiencies of the previously described radar based anti-missile system. The Laser, an acronym for light amplification by the stimulated emission of radiation, produces radiant energy, generates a beam of coherent light that follows a straight line to a target and illuminates that target. At high power levels characteristic of laser weapons, the laser beam heats the target within a short time to destructive levels.
Laser energy that strikes a missile must cause catastrophic failure. Heating a site on the missile to the point that it is sufficiently weakened, causes the missile to fall apart. By heating the missile's protective re-entry material, it is unable to withstand the re-entry forces and falls apart. In some instances the guidance system is destroyed so the missile becomes unguided. At the velocities involved, loss of guidance can also cause structural failure.
Difficulties caused by the effects of the atmosphere have been encountered in delivering to the attacking missile the required amount of laser energy to cause its destruction. The problem of directing a high energy laser beam is the formation of a diverging lens along the beam path in front of the laser as the beam moves through the atmosphere to the attack missile. This is known as "thermal blooming". It decreases the effective power that can be delivered to a site on an object in the atmosphere.
An explanation of thermal blooming resides in the heat generated immediately in the path of the laser beam. The laser radiation striking the air is converted to heat causing the air path temperature to increase. The air in the beam path expands and rises. As cross currents of air enter the beam path, they are also heated and leave the beam path on the down wind side. This changes the density of heated air, produces air expansion and encourages the influx of colder air. Changes in air density causes changes in the refractive index of the air immediately in advance of the beam path. The index of refraction of air is proportional to molecular density causing the hottest regions of the beam path to have a reduced index of refraction. Refractionive index variations create a lens effect that cause the radiation to diverge or spread out from the original direction--to bloom. Blooming progressively increases the diameter of the laser beam as it moves out from the laser generator.
By the time the laser beam strikes the incoming missile it is sufficiently diffuse and its energy is no longer sufficiently focused to heat to the required temperature levels any specific site on the missile to destroy it. Known efforts to minimize thermal blooming have been largely ineffective. One approach has been to increase the power. Higher power is ineffective to overcome the blooming effect.
Generally, chemical lasers can generate at the power necessary to bring down the missile. Chemical type lasers and the associated equipment necessary for the defense weapon are quite costly. These lasers have the advantage of being physically smaller in size and, hence, are mobile. In contrast known lasers that can deliver high power are too large to be mobile and usually used from fixed positions.
An object of the invention, therefore, is to provide a new defensive weapons system and a method to effectively destroy offensive missiles.
An additional object is to provide a high powered laser defense system that is capable of mobile mounting so that it may be more quickly deployed to different locations.
A still additional object of the invention is to provide a defense system using laser weapons of existing design to create laser beams that can be transmitted through the earth's atmosphere and yet be capable of destroying attack missiles.
A further object of the invention is to avoid or surmount thermal blooming effects limiting the effectiveness of laser weapons against distant targets as may be located within or are accessible only by going through the earth's atmosphere.